This study is an attempt to construct a theoretical and descriptive framework for the analysis of lexicogrammatical, semantic and semiotic cohesion, called the Extended Systemic Cohesive Model. This model is an extension of the Halliday-Hasan model (1976) whose descriptive range is limited to lexicogrammatical cohesion. The classical hypothesis that cohesion is realized through the lexicogrammatical system is proved to be inadequate. An alternative thesis is proposed and justified: that cohesion is captured at lexicogrammatical, semantic and semiotic levels. As a result, a linguistic framework is constructed which explicitly accounts for the properties that make a text hang together at these three particular levels, and its applicability is tested against given empirical data. The discussion is focused on how and why the above three types of cohesion contribute to the unity of a text plus a critical review of previous relevant work.